The present invention relates to gas turbine engines, and in particular, to alternators on gas turbine engines. Gas turbine engines typically have at least one spool that includes a compressor and a turbine. An accessory gearbox is often connected to the spool, and provides gearing to connect the spool to various accessories, such as alternators, pumps, and engine starters, for example. Each accessory is typically connected directly to the gearbox. Thus, as more accessories are added to the gearbox, the size and weight of the gearbox can become undesirably large and heavy. This can be particularly undesirable in applications where space is a premium and weight is undesirable, such as with a gas turbine engine used on an aircraft.
Some gas turbine engines have a relatively small permanent magnet alternator (PMA) attached to the gearbox and driven by the spool. Such an alternator typically supplies electric power either primarily or exclusively to an engine controller. One or more larger generators typically power other systems on the aircraft. These permanent magnet alternators allow for an engine controller to have a relatively reliable supply of power whenever the spool is rotating, but also occupy valuable space on the accessory gearbox.
Gas turbine engines also typically have various components, such as gears and bearings, which benefit from lubrication and cooling. An oil supply system supplies oil, or another lubricating liquid, to and from the components to lubricate and cool the components. A typical method of cooling engine oil is by utilizing an air-to-oil heat exchanger. A common source of air for a heat sink is bypass flow from an engine propulsion fan. If the bypass flow is relatively slow, the heat exchanger typically needs to be relatively large and bulky to achieve the desired amount of cooling. A relatively large heat exchanger undesirably increases the weight of an aircraft. In gas turbine engines where the heat exchanger is positioned in a bypass flow stream of the engine's propulsion fan, the heat exchanger can also reduce overall thrust output.